The present invention is directed toward automotive transmission testing and, more particularly, toward an apparatus for testing on/off solenoid valves and proportional or linear solenoid valves of an automotive transmission.
An automatic transmission for an automotive vehicle automatically shifts gears based on certain operating conditions, such as crankshaft speed, accelerator pedal depression, vehicle speed, etc. The shifting of gears is performed by clutches which are actuated by pressurized hydraulic fluid. The supply of hydraulic fluid to the clutches is controlled and regulated by hydraulic circuits that include a number of control devices, such as on-off solenoid valves and proportional solenoid valves. Solenoid valves are electro-mechanical devices that utilize a solenoid to control valve activation. As is well known, a solenoid comprises a coil of wire that is wound around a movable plunger or armature that is at least partially ferromagnetic. When a given amount of current passes through the coil, the coil generates a magnetic field that moves the armature, thereby moving a seat that opens and closes the valve. In an on-off solenoid, the seat may be disposed in only two positions, namely a fully open position and a fully closed position, whereas in a proportional solenoid valve, the seat may disposed in intermediate positions between a fully open position and a fully closed position. In a proportional solenoid, the amount of movement of the armature and, thus, the position of the seat is dependent on the amount of current flowing through the coil. More specifically, the position of the seat is proportionally related to the current.
In automotive transmissions, an on-off solenoid valve is used to either selectively close a hydraulic circuit to produce a maximum pressure therein, or to open a hydraulic circuit to produce a minimum pressure therein. The engagement and disengagement of a clutch to shift between gears is typically accomplished by moving between maximum and minimum pressures in a hydraulic circuit through the activation and deactivation of on-off solenoid valves. Such on-off solenoid valves are typically referred to as shift solenoid valves. Shift solenoid valves are typically actuated by electrical signals having a voltage in a range between 5 and 18 volts direct current.
In automotive transmissions, a proportional solenoid valve is used to vary the fluid pressure in a hydraulic circuit. The engagement and disengagement of a start clutch, which controls motive power transmission when a vehicle is started or stopped, is often controlled by varying fluid (oil) pressure in a hydraulic circuit using proportional solenoid valves. Proportional solenoid valves may also be used for shift control and for PH-PL control (pressure high—pressure low). Such proportional solenoid valves are typically controlled by electrical signals having a current varying between 0 and 2 amps.
In an automotive transmission, solenoid valves are typically mounted to a transmission valve body that includes worm trails and passages through which hydraulic fluid is routed. The transmission valve body and the solenoid valves are disposed inside a transmission case.
Since defects in the solenoid valve and associated hydraulic circuits will cause an automatic transmission to malfunction, it is important to verify that all solenoid valves and associated hydraulic circuits are operating properly before they are installed in a transmission during the assembly of the transmission. It is also important to be able to identify a defective solenoid and/or associated hydraulic circuit when repairing a malfunctioning transmission. Accordingly, devices for testing automatic transmissions and automatic transmission solenoid valves have been developed. Many of these devices are operable only to test shift solenoid valves. Some of these devices, however, can test both a shift solenoid and a proportional solenoid. For example, U.S. Pat. No. 5,712,434 to Sylvis and U.S. Pat. No. 6,038,918 to Newton each disclose a testing device that can test both a shift solenoid and a proportional solenoid. Each device, however, can only test one shift solenoid or one proportional solenoid at a time. Moreover, in each device, a proportional solenoid is tested by varying the current supplied to coil of the proportional solenoid by manipulating a potentiometer knob. Thus, when testing a plurality of proportional solenoid valves, a considerable amount of time is wasted adjusting the potentiometer knob to produce the various test current levels. Moreover, many of these knob-type potentiometers are not smooth, which can lead to inaccuracies.
Based on the foregoing, there exists a need in the art for an improved test apparatus for testing shift solenoid valves and proportional solenoid valves of an automatic transmission. The present invention is directed to such a test apparatus.